The long term goals of this proposal are twofold: the first is to study the origin and differentiation of neuroglia in the central nervous system and the second is to determine the underlying cause of the myelin deficiency in the mutant mouse jimpy (jp). The lineage and differentiation of neuroglial cells is a complex process which begins with undifferentiated cells in the neuroepithelium and ends, after numerous cell divisions, in the formation of the two macroglial cell types: astrocytes and oligodendrocytes. Both of these cell types acquire over time a unique set of markers which distinguish one from the other. To understand the differentiation of neuroglia, it is essential to determine the sequence of expression of these markers in macroglia and to relate this information to cell division. In one set of experiments employing immunocytochemistry and autoradiography, antibodies to astroglial and oligodendroglial cell specific proteins will be utilized to determine which of these markers are expressed by cells incorporating radioactive thymidine. The information obtained from this study will permit conclusions as to whether cell differentiation has already begun in the dividing cells and as to whether two distinct cell lineages exist in postnatal rodent brain. In another set of experiments, colloidal gold immunocytochemistry and electron microscopy will be employed to determine whether an individual glial cell can express both an astroglial and an oligodendroglial specific marker. Other in vivo experiments are designed to determine whether astrocytes arise in two distinct waves, one before oligodendrocytes and one after. The study of the jp mutant will focus upon early differentiation of the oligodendrocyte as this cell has been shown to undergo premature and massive cell death in jp and to exhibit cell cycle abnormalities. Autoradiographic studies will examine key features of the the cell cycle to determine when the block occurs and whether they actually undergo division. Other studies will determine the length of their survival. This information will be correlated with the expression of proteolipid protein as the message for it is defective in jp. Cultures prepared from jp brains will be manipulated to determine what cell type is responsible for "rescuing" the jp oligodendrocytes exposed to conditioned media. The in vivo and in vitro studies will provide data which will help elucidate the sequence of events leading to myelin deficit.